The document provides guidelines for establishing a herbicide program for corn and soybean crops incorporating cover crops while detailing the impacts of herbicide residues, crop rotation restrictions, and soil and climatic factors on herbicide persistence. It outlines various herbicides' durations, suitable application strategies, and necessary precautions to prevent crop injury and manage specific weed challenges like giant ragweed. Recommendations emphasize the importance of adhering to label instructions and adjusting herbicide use based on specific crop and cover crop interactions.

1. Setting up a Corn and
Soybean Herbicide Program
with Cover Crops
Jeff Stachler
Extension Educator
3-3-20 (2020 CTC)

2. • Injury / death of cover crop
• Herbicide residues for feed
– Crop rotation restrictions must be followed
– Label is a legal document
– Few species can be planted for feed for
certain products
Two reasons for crop rotation

3. • Length of time herbicide remains active in
soil.
• Driven by disappearance or breakdown of
herbicide.
• Factors affecting persistence.
– Soil factors
– Climatic conditions
– Herbicidal properties
Soil persistence / Soil residual life
From: Persistence of Herbicides in Soil; 1-1-99; Curran; Penn State Extension

4. • Soil composition
– Soil texture
• Clay
– Organic matter
• Soil chemistry
– Soil pH
• Too high
– Atrazine and some ALS herbicides
• Too low
– Imadazolinones
– Chemical and/or microbial breakdown
• Moisture, temperature, pH, oxygen, and mineral nutrient
supply drive microbial breakdown
Soil factors

5. • Moisture
– Biggest driver
– Both microbial and chemical breakdown
• Temperature
– Warmer temperature more microbial and
chemical breakdown
• Sunlight
– Chemical and/or microbial breakdown
• Moisture, temperature, pH, oxygen, and mineral
nutrient supply drive microbial breakdown
Climatic factors

6. • Water solubility
– Leaching occurs when herbicide is dissolved
in water and moves downward in soil profile
• Vapor pressure
– Herbicide changes from liquid or solid to gas
• Chemical structure
Herbicide properties

7. • Imazethapyr (Pursuit, Authority
Assist/Sulfentazone Assist, Extreme, Matador,
Panther Pro, Pummel, Torment, Zidua Pro, Latir)
– 40 months
• Radish
• Kale
• Rape
• Turnip
• Mustards
• Buckwheat
– 18 months
• Oat
• Sunflower
• Sorghum
Herbicides with extra long rotation

8. • Chlorimuron (Classic, Canopy, Authority MAXX,
Authority XL / Zone, Cloak, Canopy Blend,
Canopy EX / Cloak EX / Fallout, Enlite, Envive,
Fierce XLT, Synchrony XP, Trivence, Valor XLT)
– 18 months
• Radish
• Kale
• Rape
• Turnip
• Mustards
• Buckwheat
• Sunflower
– 12 months
• Legumes
Herbicides with extra long rotation
Over 7 pH, then maybe longer

9. • Cloransulam (FirstRate, Authority First /
Sonic, Surveil)
– 30 months
• Sunflower
– 18 months
• Rape
• Other mustard species
• Buckwheat
– 12 months
• barley
Herbicides with extra long rotation

10. • Sulfentrazone (Spartan, Authority Assist /
Sulfentrazone Assist, Authority First / Sonic,
Authorit MAXX, Authority MTX, Authority XL /
Zone, Authority Supreme)
– 24 months
• Rape
• Other mustard species
Herbicides with extra long rotation

11. • fomesafen (Flexstar, Flexstar GT, Marvel,
Prefix, Torment, Warrant Ultra)
– 24 months
• Rape
• Other mustard species
Herbicides with extra long rotation

12. • Glyphosate + ALS – resistant
– marestail
• Glyphosate + ALS + PPO – resistant
– Common ragweed
– Giant ragweed
– Waterhemp
Weed control assumptions

13. • Burndown
–Glyphosate + Sharpen/Zidua PRO + 2,4-D (+ metribuzin)
–Gramoxone (4 pt) + 2,4-D + metribuzin
–Glyphosate + dicamba (Xtend soybeans)
–Glyphosate + dicamba + Sharpen (Xtend soybeans)
–Glufosinate + Sharpen + metribuzin
–Glufosinate + 2,4-D + metribuzin
• Control in spring without a fall application
Winter cereal grain species - soybean

14. • PRE
– All can be used
• Slight concerns
– Authority First / Sonic
– Metribuzin
– Metolachlor
– Pyroxasulfone (maybe largest concern)
– Prefix
– Especially with dry weather
Winter cereal grain species - soybean

15. • POST
– Glyphosate + dicamba (Xtend soybean)
– Glufosinate + 2,4-D (E3 soybean)
– Glufosinate (LL, E3, and GT27 soybeans)
– Glyphosate + 2,4-D (E3 soybean)
• Weakest on waterhemp and marestail
– Assure II / Targa not likely (120 days)
– Clethodim (30 days)
– Fusilade
– Flexstar and Cobra if no PPO resistance
Winter cereal grain species - soybean

16. • Burndown
–Glyphosate + Sharpen + 2,4-D (+ metribuzin)
–Gramoxone (4 pt) + 2,4-D + metribuzin
–Glyphosate + dicamba (Xtend soybeans)
–Glyphosate + dicamba + Sharpen (Xtend soybeans)
–Glufosinate + Sharpen + metribuzin
–Glufosinate + 2,4-D + metribuzin
• Control in spring without a fall application
Tillage radish and other mustard species - soybean

17. • PRE
– Spartan
• Slight concerns based upon label
– Valor
– Metribuzin
– Metolochlor
– Pyroxasulfone
Tillage radish and other mustard species - soybean

18. • POST
– Glyphosate + dicamba (Xtend soybean)
– Glufosinate + 2,4-D (E3 soybean)
– Glufosinate (LL, E3, and GT27 soybeans)
– Glyphosate + 2,4-D (E3 soybean)
• Weakest on waterhemp and marestail
– Assure II / Targa not likely
– Clethodim
– Fusilade
– Cobra if no PPO resistance
Tillage radish and other mustard species - soybean

19. • Burndown
–Glyphosate + Sharpen + 2,4-D (+ atrazine 1.5 lb ai/A)
–Gramoxone (4 pt) + 2,4-D + atrazine 1.5 lb ai/A
–Glufosinate + Sharpen + atrazine 1.5 lb ai/A
–Glufosinate + 2,4-D + atrazine 1.5 lb ai/A
• Control in spring without a fall application
Winter cereal grain species - corn

20. • PRE
– All can be used
• Slight concerns
– Pyroxasulfone (maybe largest concern)
– mesotrione
Winter cereal grain species - corn

21. • POST
– All HPPD herbicides
– Clopyralid
• Not waterhemp
– Dicamba
– 2,4-D
– Glufosinate (LL corn)
– Slight concerns
• Mesotrione
• Tembotrione
Winter cereal grain species - corn

22. • LL corn
– Glufosinate 32 to 43 fl oz/A
• RR + LL corn
– Glufosinate 32 to 43 fl oz/A
– + glyphosate 1.125 lb ae/A
• Maybe for cereal rye not for feed apply 1.5
oz/A flumioxazin 7 days before planting
• If planting broadleaf and grass crop, then no
PRE herbicide, especially if used for feed
Herbicide programs for inter-seeding cover crop
into corn

23. 1. Look at label to determine if herbicide can be
used on cover crops for feed.
2. Must control the troublesome weeds without
injuring or killing cover crop
Summary

24. Thank you
Are there any questions??
Jeff Stachler
stachler.1@osu.edu

25. • Materials and methods
– Herbicide applications
• Burndown herbicide
– 5-8-19
– Glufosinate (Cheetah) (34 fl oz/A) plus Fusilade DX
(10 fl oz/A)
– Adjuvant = ammonium sulfate 3.0 lb/A
• Preemergence (PRE)
– 5-8-19
– 0; Valor (2.5 oz/A); Fierce XLT (4.5 oz/A); and
Authority Supreme (8 fl oz/A)
Herbicide applications in 2,4-D-resistant soybean

26. • Materials and methods
– Herbicide applications
• Postemergence (POST)
– No PRE; 6-26-19
– Valor; 6-28-19
– Fierce XLT & Authority Supreme; 7-10-19
– Cheetah (34 fl oz/A); Roundup WeatherMAX (32
fl oz/A); Enlist One (32 fl oz/A)
– Adjuvant = ammonium sulfate (3 lb/A - Cheetah
& 1.7 lb/A - Roundup)
– Weed size
» 0.1” to 12”; average = 5”
Herbicide applications in 2,4-D-resistant soybean

27. Herbicide applications in 2,4-D-resistant soybean
Treatment 49 DAT (6-26) 28 DAT POST
0 fb Cheetah 0 f
0 fb Roundup 0 f
0 fb Cheetah + Enlist One 0 f
0 fb Roundup + Enlist One 0 f
Valor fb Cheetah 54 e
Valor fb Roundup 58 de
Valor fb Cheetah + Enlist One 61 d
Valor fb Roundup + Enlist One 58 de
Fierce XLT fb Cheetah 78 bc
Fierce XLT fb Roundup 73 c
Fierce XLT fb Cheetah + Enlist One 74 c
Fierce XLT fb Roundup + Enlist One 81 ab
Authority Supreme fb Cheetah + Enlist One 87 a

28. Herbicide applications in 2,4-D-resistant soybean
Treatment 49 DAT (6-26) 28 DAT POST
0 fb Cheetah 0 f 51 d
0 fb Roundup 0 f 10 f
0 fb Cheetah + Enlist One 0 f 80 bc
0 fb Roundup + Enlist One 0 f 74 c
Valor fb Cheetah 54 e 85 ab
Valor fb Roundup 58 de 23 e
Valor fb Cheetah + Enlist One 61 d 94 a
Valor fb Roundup + Enlist One 58 de 90 ab
Fierce XLT fb Cheetah 78 bc 45 d
Fierce XLT fb Roundup 73 c 9 f
Fierce XLT fb Cheetah + Enlist One 74 c 84 ab
Fierce XLT fb Roundup + Enlist One 81 ab 94 a
Authority Supreme fb Cheetah + Enlist One 87 a 92 a

29. • PRE (high rates & 2 to 4 ai’s) fb 1 POST
– Soybean injury likely
– May need a 2nd POST
• PRE fb 2 POST
– Same POST herbicide will lead to resistance
– 2nd POST may be too late for soybean stage
• Liberty = R1; dicamba = R1; fomesafen = R1 and only
one application; Enlist One = R2
• PRE fb POST + Residual
– Need rain to active
– Existing plant MUST be controlled
Herbicide strategies

30. • Site 14 (PPO)
– Flumioxazin (2.5 oz), sulfentrazone (8 fl oz)
• Site 5 (PSII)
– Metribuzin (8 oz/A / 12 fl oz)
• Site 15 (mitosis inhibitor)
– Metolachlor (1.5 pt), acetochlor (1.5 qt), pyroxosulfone
(4.08 fl oz), dimethanamid (18 fl oz)
• Site 7 (PSII)
– Linuron (1.5 to 2 lb/A)
• Site 3 (Mitotic inhibitors)
– Pendimethalin (2.4 pt)
PRE AI’s available

31. • Glyphosate
– Resistance in most populations
• Fomesafen, lactofen, and acifluorfen
– Resistance in some populations
• Glufosinate
– No resistance and not perfect
• Dicamba
– No resistance and not perfect
• 2,4-D
– Resistance in MO, IL, NE and not perfect
POST AI’s

32. • Stage
– 3rd trifoliate – Dual II Magnum
– 90 days PHI – Dual Magnum
– 5th trifoliate – Outlook, Parallel
– 6th trifoliate - Zidua
– R2 – Warrant
• Maximum rate
– Dual II Magnum - 2.5 pt/A
– Parallel - 2.55 pt/A
– Outlook – 24 fl oz/A
– Zidua – 5.75 fl oz/A
– Warrant – 4 qt/A
Limitations with POST residuals

35. Why is giant ragweed difficult to manage?
Good amount of genetic diversity –
monoecious
Germination period is increasing, especially
late
Too few effective herbicides in soybean
Timing of POST herbicides, not always
correct
Herbicide resistance
– Sites 2, 9, 14

36. Strategy for giant ragweed in soybean
 PRE fb POST fb POST
 PRE contains the following
– Chlorimuron / cloransulam /
imazaquin / imazethapyr
– Flumioxazin ??
– Metribuzin ??
– Sulfentrazone = 0!

37. Strategy for giant ragweed in soybean
 PRE fb POST fb POST
 POST
– Glyphosate
Resistance!!
– Fomesafen / lactofen
Resistance!!
– FirstRate ??
Resistance!!
– Glufosinate
– Dicamba
– 2,4-D

38. Strategies for giant ragweed in corn
 PRE fb POST
– Comprehensive PRE
Atrazine (1.6 to 2) + Balance,
Callisto, Stinger or Acuron
– POST
Status, DiFlexx, DiFlexx Duo +
atrazine (??)
Others – Impact, Laudis,
Callisto, Shieldex + atrazine

39. Strategies for giant ragweed in corn
 Early POST only
– Corvus + atrazine (high rate) to
< V2 corn
– 3-4” giant ragweed, < 12” corn
Capreno, Resicore, others +
atrazine, Acuron
– Concerned about timing - yield
loss